1. Field of the Invention
The present invention relates to a transmission rate control method for controlling, at a mobile station, a transmission rate of uplink user data, in a radio communication system capable of controlling a transmission rate of uplink user data based on an absolute transmission rate of uplink user data which is transmitted via an absolute transmission rate control channel and a relative transmission rate of uplink user data which is transmitted a relative transmission rate control channel, and a mobile station, a radio base station, and a radio network controller used in the transmission rate control method.
2. Description of the Related Art
In a conventional mobile communication system, when setting a Dedicated Physical Channel (DPCH) between a mobile station UE and a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of uplink user data, in consideration of hardware resources for receiving of the radio base station Node B (hereinafter, hardware resource), a radio resource in an uplink (an interference volume in an uplink), a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the uplink user data by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of uplink user data (for example, per approximately 1 through 100 ms), due to the increase of processing load and processing delay in the radio network controller RNC.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the uplink user data can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the uplink user data is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the uplink radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Referring to FIG. 3, the mobile communication system, to which the “Enhanced Uplink” is applied, will be described.
In an example of FIG. 3, the cell #3 controlled by the radio base station Node B #1 is a serving cell for a mobile station UE, which mainly controls the transmission rate of uplink user data transmitted by the mobile station UE.
The cell #4 controlled by the radio base station Node B #2 is a non-serving cell for the mobile station UE, which sets a radio link with the mobile station UE as well as the serving cell.
In the above mobile communication system, the cell #3 (the serving cell for the mobile station UE) is configured to transmit, to the mobile station UE, an “Enhanced Absolute Grant Channel (E-AGCH, absolute transmission rate control channel)” for transmitting an absolute transmission rate of uplink user data and an “Enhanced Relative Grant Channel (E-RGCH, relative transmission rate control channel)” for transmitting a relative transmission rate of uplink user data (for example, UP Command or DOWN Command).
Further, in the above mobile communication system, the mobile station UE is configured to transmit an “Enhanced Dedicated Physical Control Channel (E-DPCCH)” and an “Enhanced Dedicated Physical Data Channel (E-DPDCH)” to the cell #3 (the serving cell).
Furthermore, in the above mobile communication system, the cell #4 (the non-serving cell for the mobile station UE) is configured to transmit the E-RGCH to the mobile station UE.
Here, in the above mobile communication system, the radio network controller RNC is configured to notify, to the mobile station UE, the information for identifying the E-RGCH transmitted from the cell #3 (the serving cell for the mobile station UE) and the information for identifying the E-AGCH transmitted from the cell #3 (the serving cell for the mobile station UE), when the mobile station UE establishes a data connection (a Dedicated Channel (DCH)/E-DPDCH) for transmitting uplink user data. Such information includes channelization codes, sequence pattern, and the like.
Then, the mobile station UE is configured to perform a receive processing of the E-RGCH, which is transmitted from the serving cell, using the channelization codes and the sequence pattern for the E-RGCH. When the mobile station UE cannot determine the relative transmission rate of the uplink user data transmitted via the E-RGCH, the mobile station UE is configured to maintain the transmission rate of the uplink user data. When the mobile station UE can determine the relative transmission rate of the uplink user data transmitted via the E-RGCH (UP Command or DOWN Command), the mobile station UE is configured to change the transmission rate of the uplink user data based on the determined result.
By the way, a mobile communication system in which the serving cell transmits only the E-AGCH and does not transmit the E-RGCH so as to decrease loads in radio downlink can be considered.
However, in the mobile communication system, the E-RGCH will be defined in the mobile station UE when the mobile station UE establishes a data connection (DCH, E-DPDCH) for transmitting the uplink user data, in general. Accordingly, there has been a problem that the mobile station UE cannot determine whether or not the serving cell is transmitting the E-RGCH.
In other words, the mobile station UE may detect the E-RGCH erroneously due to noise and the like, and may change the transmission rate of the uplink user data unnecessarily, even when the serving cell does not transmit the E-RGCH. Accordingly, there has been a problem that the utilization efficiency of radio resources may be decreased.